netdev - Re: [PATCH bpf-next v2 1/2] tools: bpftool: clean up function to dump map entry

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Date:   Tue, 8 Sep 2020 20:25:44 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Quentin Monnet <quentin@...valent.com>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        bpf <bpf@...r.kernel.org>, Networking <netdev@...r.kernel.org>
Subject: Re: [PATCH bpf-next v2 1/2] tools: bpftool: clean up function to dump
 map entry

On Mon, Sep 7, 2020 at 9:36 AM Quentin Monnet <quentin@...valent.com> wrote:
>
> The function used to dump a map entry in bpftool is a bit difficult to
> follow, as a consequence to earlier refactorings. There is a variable
> ("num_elems") which does not appear to be necessary, and the error
> handling would look cleaner if moved to its own function. Let's clean it
> up. No functional change.
>
> v2:
> - v1 was erroneously removing the check on fd maps in an attempt to get
>   support for outer map dumps. This is already working. Instead, v2
>   focuses on cleaning up the dump_map_elem() function, to avoid
>   similar confusion in the future.
>
> Signed-off-by: Quentin Monnet <quentin@...valent.com>
> ---
>  tools/bpf/bpftool/map.c | 101 +++++++++++++++++++++-------------------
>  1 file changed, 52 insertions(+), 49 deletions(-)
>
> diff --git a/tools/bpf/bpftool/map.c b/tools/bpf/bpftool/map.c
> index bc0071228f88..c8159cb4fb1e 100644
> --- a/tools/bpf/bpftool/map.c
> +++ b/tools/bpf/bpftool/map.c
> @@ -213,8 +213,9 @@ static void print_entry_json(struct bpf_map_info *info, unsigned char *key,
>         jsonw_end_object(json_wtr);
>  }
>
> -static void print_entry_error(struct bpf_map_info *info, unsigned char *key,
> -                             const char *error_msg)
> +static void
> +print_entry_error_msg(struct bpf_map_info *info, unsigned char *key,
> +                     const char *error_msg)
>  {
>         int msg_size = strlen(error_msg);
>         bool single_line, break_names;
> @@ -232,6 +233,40 @@ static void print_entry_error(struct bpf_map_info *info, unsigned char *key,
>         printf("\n");
>  }
>
> +static void
> +print_entry_error(struct bpf_map_info *map_info, void *key, int lookup_errno)
> +{
> +       /* For prog_array maps or arrays of maps, failure to lookup the value
> +        * means there is no entry for that key. Do not print an error message
> +        * in that case.
> +        */

this is the case when error is ENOENT, all the other ones should be
treated the same, no?


> +       if (map_is_map_of_maps(map_info->type) ||
> +           map_is_map_of_progs(map_info->type))
> +               return;
> +
> +       if (json_output) {
> +               jsonw_start_object(json_wtr);   /* entry */
> +               jsonw_name(json_wtr, "key");
> +               print_hex_data_json(key, map_info->key_size);
> +               jsonw_name(json_wtr, "value");
> +               jsonw_start_object(json_wtr);   /* error */
> +               jsonw_string_field(json_wtr, "error", strerror(lookup_errno));
> +               jsonw_end_object(json_wtr);     /* error */
> +               jsonw_end_object(json_wtr);     /* entry */
> +       } else {
> +               const char *msg = NULL;
> +
> +               if (lookup_errno == ENOENT)
> +                       msg = "<no entry>";
> +               else if (lookup_errno == ENOSPC &&
> +                        map_info->type == BPF_MAP_TYPE_REUSEPORT_SOCKARRAY)
> +                       msg = "<cannot read>";
> +
> +               print_entry_error_msg(map_info, key,
> +                                     msg ? : strerror(lookup_errno));
> +       }
> +}
> +

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